A polarizer element, particularly a polarizing beam splitter, is an element in which a specific polarized light is obtained by changing the direction of light propagation between polarized lights perpendicular to each other. Such an element is used as a component for constructing an optical isolator or an optical circulator in a light source module for an optical fiber communication system, an optical head for an optical disc and so on.
A conventional polarizing beam splitter such as Glan-Thompson prism or Rochon prism is an element in which a light path is split based on the difference between the refraction angles or the total reflection angles of two orthogonally polarized light components at the reflection plane of a crystal with large birefringence, or an element in which light is totally reflected or transmitted in accordance with the difference of refractive indices of polarization light in multilayer dielectric film formed at the reflection plane of a total reflection prism consisting of an isotropic optical medium, such as glass.
According to the conventional polarizer element, however, there is a disadvantage that the size is large because the configuration is a cube having a side as long as .sqroot.2 times a diameter of a transmitting light beam. This is because the conventional polarizer element has a reflection boundary surface which is positioned to be slant relative to a light axis by at least 45 degrees. In more detail, where the conventional polarizer element is applied to an optical disc for recording and reproducing, a transmitting light beam is large in size, so that the configuration is a cube having a side of 8 to 10 mm.
Another type of a conventional polarizer element is disclosed in "National conference record, 1982, Optical & Radio wave Electronics, the Institute of Electronics & Communication Engineers of Japan, Part 2". The conventional polarizer element consists of a birefringent tapered plate of Rutile (TiO.sub.2) having a tapered angle of 4 degrees. When parallel light beam is incident to the birefringent tapered plate on one side thereof, the parallel light beam is subject to different refractions between an extraordinary ray component and an ordinary ray component, so that the two components are split on the other side of the birefringent tapered plate with a split angle of approximately 1 degree.
According to the birefringent tapered plate, however, there is a disadvantage that a fabricating process is complicated because the cutting of a tapered configuration is difficult on a mass-production basis, and the polishing of a tapered surfaces is also difficult to be carried out. There is a further disadvantage that Rutile is expensive.